Sheila Royeras, her husband, her mother and two young daughters live in a single-room cement apartment in a poor neighborhood in Manila, Philippines. Like many such homes, it's mostly dark during the day, except for a small ray of sunlight that enters through an open front door.

But this is about to change.

On this morning, volunteers and local government workers arrive to hang low-tech solar light bulbs from the corrugated metal roof. The bulbs are very simple, very effective and the ambitious plan is to put them in 1 million homes this year.

The bulbs are actually discarded plastic soda bottles filled with water and wedged in a hole cut in the roof. With the help of a tropical sun, the makeshift bulbs give off about 55 watts of light. There is no electricity involved.

As a result, electricity bills are slashed in a poor country where nearly half the population lives on less than $2 a day.

While the workers install the light bulbs in her home, Royeras looks forward to keeping the electric lights off during the day.

"Because of [the high price of] electricity sometimes we don't eat," she says. "If we don't pay that bill on time, electricity is cut."

Royeras says having electricity is a priority because her sixth-grader needs light to study and keep up her honor-roll status.

A Simple Bulb

The holes in the roof are cut to the size of a one-liter plastic soda bottle. The workers fill the bottle with purified water and two caps of bleach that prevent the growth of mold. The bottle is held in place by a small metal brace.

Nelly Duka, a community leader who helps assemble the bulbs, says they have a five-year lifespan.

Volunteers push the bottle through the hole in the roof until it juts in halfway. They hammer the brace to keep it in place. Then, workers use sealant to guard against leaks from rain. The sun's light passes through the top of bottle and the water inside refracts it, casting a glow from the bottom.

In a neighboring municipality, Illac Diaz keeps tabs on a solar bulb-making program at a local jail. Diaz heads the nonprofit MyShelter Foundation, which is overseeing this lighting project called "A Liter of Light."

He says in tropical countries poor people often live in dark spaces that are heavily covered against driving rains and the hot sun. Diaz says this type of bulb is a better alternative to candles or other potential fire hazards.

"It's safer. It's healthier. It's brighter. And the funny thing is the light bulb actually comes from the place you'd least expect it, which is the trash bin," Diaz says. "So it's the cheapest light bulb in the world."

Diaz estimates the solar bulbs will save customers an average of $10 a month on their electric bills.

For Royeras, having the three new bulbs in her tiny house is a huge benefit.

"I'm much happier," she says. "Maybe by the time we get the next electric bill, I'll have some extra money to buy food."

Copyright 2012 National Public Radio. To see more, visit http://www.npr.org/.

Transcript

ROBERT SIEGEL, HOST:

From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel. In the Philippines, a Manila-based solar lighting project is outfitting a million houses with new light bulbs and they aren't the kind of light bulbs you might expect. They are simpler: just used, plastic bottles and water. They're meant to not only help the poor light their homes, but to save them money, too, in a country where nearly half the population lives on less than $2 a day.

Producer Simone Orendain visited a recent installation in Manila.

SIMONE ORENDAIN, BYLINE: During the day, a small ray of sunlight enters through an open front door and partly illuminates the Royeras home. The 200-square-foot, cement apartment is in the shadow of taller neighboring houses, but the mostly dark interior is about to change. On this morning, volunteers and local government workers pile in to hang some low-tech light bulbs from the corrugated metal roof.

Sheila Royeras, her husband, her mother and two young daughters live in this single room. While the volunteers work, she looks forward to keeping the electric lights off in the daytime.

SHEILA ROYERAS: (Foreign Language Spoken).

ORENDAIN: She says, because of the high price of electricity, sometimes the family doesn't eat and, if they don't pay the bill on time, electricity is cut. Royeras says having electricity is a priority, especially at night because her sixth grader needs light to study by to keep up her honor roll status.

The first hole in the roof is cut. It's exactly the diameter of a plastic one liter soda bottle. The volunteers fill a liter bottle with purified water and two capsules of bleach. The bottle is held in place by a small metal brace.

Nelly Duka is a community leader who learned how to assemble the bulbs. She says the bottle bulbs have a five year lifespan.

NELLY DUKA: The bottles off of using bleach. Yes. (Unintelligible) molds. The insects, also, and the water will remain clear.

ORENDAIN: Volunteers push the bottle through the hole in the roof until it juts halfway in. They hammer its brace into place, then workers use sealant to guard against leaks from rain. The sun's light passes through the top of the bottle and the water inside refracts it, casting a 55 watt glow from the bottom.

In a neighboring municipality, Illac Diaz keeps tabs on a solar bulb making program at a local jail. Diaz heads the nonprofit My Shelter Foundation, which is overseeing this lighting project called A Liter of Light. He says, in tropical countries, poor people often live in dark spaces that are heavily covered against driving rains and the hot sun. Diaz says this type of bulb is a better alternative to candles or other potential fire hazards.

ILLAC DIAZ: It's safer, it's healthier, it's brighter and the funny thing is the light bulb actually comes from the place you didn't expect it, which is the trash bin. So it's the cheapest light bulb in the world.

ORENDAIN: Diaz estimates the solar bulbs will save customers an average of $10 a month on their electric bills. For Sheila Royeras, having the three new bulbs in her tiny house is a godsend.

ROYERAS: (Foreign Language Spoken).

ORENDAIN: I'm much happier, she says with a big smile, and she adds, maybe when they pay next month's electric bill, they'll have money left over to buy food with.

For NPR News, I'm Simone Orendain in Manila. Transcript provided by NPR, Copyright National Public Radio.